The leaves on my azaleas are turning white. They look dirty underneath, too. How can I stop this?
Your azaleas are infested with lace bugs. These ubiquitous insects insert their mouth parts into leaf undersides and suck out the chlorophyll. Each piercing makes a pale spot, known as stippling, and eventually the entire leaf can turn yellow and fall off. The black dots under the leaves are fecal spots. Lace bugs themselves are hard to see because they have translucent "lacy" wings. Like many insects, lace bugs are attracted to stressed plants. Any azalea in sun-baked clay soil, instead of the part shade and rich moist soil which azaleas like, is guaranteed to get a damaging number of lace bugs. Healthy azaleas tolerate some lace bugs and natural predators help in control. There are multiple generations a year. Insecticidal soap, with or without pyrethrum, can be sprayed under leaves in May and again in July. Moving an unhappily located azalea may be easier.
My boxwood shrub has been healthy for 10 years, but the outer leaves turned brown last summer and now the whole plant is brown. It is in full sun and never needed water before. I did build a wood enclosure around it last year and put in new top soil, but I don't know how that would be killing it.
Your boxwood is dead as far as we can see from the photo you submitted to our website. If there are any green leaves left at all, you can try cutting it close to the ground to see if it will resprout from the root. If you raised the soil level too much, that may have buried it too deeply and suffocated the roots. Alternatively, being close to siding, it may have suffered last summer from drought or high temperatures intensified by reflection off the siding.
University of Maryland Extension's Home and Garden Information Center offers free gardening and pest information. Call 800-342-2507 or send a question to the website at hgic.umd.edu.
Plant of the week Crested Iris
It's hard to believe this ground cover is a Maryland native, what with its large flowers dominating the naturally dwarf foliage. The blue-purple and yellow flowers can be as large as half the size of the plant. A furry crest runs down each fall — the three lower petals. Its typical sword-like iris foliage reaches about 6 inches when the plant is in bloom and then continues to grow a bit taller. These beauties do well in almost full sun to partial shade in a woodsy spot where they aren't overpowered by larger plants. A pathside is ideal. The leaves rise from finger-size rhizomes that clamber over the soil at a steady pace creating a thick deer-proof mat. The rhizomes are easy to transplant and propagate. A problem-free plant, crested iris can be lightly fertilized in spring when growth commences, though compost would probably be best. — Ellen Nibali